The present invention is related to weld motion controllers and, more particularly, to an electric servo-control system for welding that has commonality from robot-to-robot and robot-to-hard-tool whether within a stand alone application or, new or retrofit robotic application.
Resistance welding is a group of welding processes in which the joining of metal is produced by the heat obtained from resistance of the work to the electric current, in a circuit of which the work is a part, and by the application of pressure. The three factors involved in making a resistance weld are the amount of current that passes through the work, the pressure that the electrode tips transfer to the work, and the time that the current flows through the work. The factor of present concern is the pressure that the electrode tips may transfer to the work. This pressure must be precise and consistent throughout the weld cycle to assure a continuous electrical circuit through the work and prevent weld splash. The pressure must further be consistently repeatable upon the next iteration of the weld cycle to assure conformity among welds.
Most resistance welding performed today is done so by robots or hard-tooled fixtures utilizing pneumatic actuators to deliver the pressure required between electrode tips. The pneumatic actuation occurs in a xe2x80x9cslam openxe2x80x9d/xe2x80x9cslam closedxe2x80x9d manner providing no precision control and no guaranteed repeatability of operation. Now that the advantages of an electric servo actuator over that of a pneumatic actuator have been realized in the areas of precision control and repeatability, it is desirable to provide these advantages in a process that is truly dependent upon control and repeatability, namely, welding.
However, an industrial welding environment can present multiple robot types as well as multiple types of welding fixtures. To retrofit each of these robots or fixtures from pneumatics to operation with an electric servo actuator would generally require an in-depth knowledge of each robot""s and each welding fixture""s own unique components, unique control system, and unique weld motion program, each requiring its own unique modifications thereto. The result is a complicated welding system running under different programs and languages, requiring different replacement parts, and costing a tremendous amount of money and time.
In an ideal situation, the various robots and fixtures would each be retrofit with the same adaptable servo-control system that could make use of the existing pneumatic input and output signals. Each adaptable servo-control system would utilize the same components, the same control systems and the same weld motion programs to limit the amount of time, knowledge, and cost required. The servo-control system would present commonality in all applications via hardware configurations yet be adaptable, through software configurations, e.g., adjustment of program parameters and recognition of existing pneumatic input and output signals, to accommodate the differences in applications.
The needs described above are in large part met by the adaptable, servo-control system for force/position actuation of the present invention. The servo-control system generally includes an electric linear actuator and a controller. The controller interfaces with the electric linear actuator and with a number of I/O signals that are independent from the electric linear actuator. The controller interface to the independent I/O signals is transparent to the manner in which the I/O signals are produced. Rather the controller simply looks for the status of the I/O that is preferably received into the controller by hard-wiring or field bus, e.g., DeviceNet I/O messaging or Profibus, such as from a industrial robot or programmable logic controller. The controller utilizes the I/O signals to select from a number of pre-established parameters to generate a motion profile for closed loop-controlled, position actuation and/or force actuation of the electric linear actuator.
In an alternative embodiment, the controller interfaces with and controls more than one electric linear actuator but does so through use of a single motion control program. The single motion control program includes a number of characterizable parameters, each of which can be independently characterized for each electric linear actuator the controller is to control. The characterizable parameters are preferably user-entered/selected through a single programming device that is connectable to the controller. In a preferred embodiment, this single programming device is a portable, programming pendant. In utilizing the I/O signals and character parameters, the controller preferably creates a bit-mapped table that is referenced by the motion control program, i.e., the bit-mapped table maps input signals to specific position or force actuations of the linear actuator.
The servo-control system is particularly suitable to resistance welding systems, whether fixture systems or industrial robot systems, where the electric linear actuator can be used to position or force actuate the welding tip of the welding gun. Again, the controller can interface with more than one electric linear actuator to effect different and independent weld operations per each electric linear actuator and can use a single motion control program with characterizable parameters per each linear actuator. The servo-control system may additionally monitor weld tip wear through various programmed operations and can observe the safety, stop operation features of a robotic welder by linking into that feature, i.e., using the controller to monitor the I/O signal enabling operation of the robot.
The controller of the servo-control system generally includes a computer and a motion controller/drive that is operably coupled to the computer. The computer receives the characterized parameters and downloads the parameters to the motion controller/drive, which then performs the operation of closed loop control of the electric linear actuator according to the hard coded program. The controller may include more than one motion controller/drive, and preferably includes one motion controller/drive per each linear actuator.